Free association norms (http://w3.usf.edu/FreeAssociation/AppendixA/index.html)

indicate that Hammer is the most common free association word for "tool" ("box" and "work" are second and third; screwdriver is 4th).

and that Red and Blue are the most common associations for color.

The arithmetic gets you into an "answer quickly" frame of mind, so you don't slowly come up with "turquoise awl".

I'm a "Red Hammer" kind of guy.